If your work has given you enough money in just one hit, what's the difference between it and those who have a specific paid day and amount when you can earn higher than them in your contract? I don't know the definition people give to stable income, but as long as there is enough to be keeping the ship sailing, it's okay to say the person is doing well.
One thing about investing in bitcoin is that the first thing is having the money you want to invest, and it should be an amount you won't be needing for a long period of time, and how long you can hold those coins that you have accumulated is based on how much you have in your reserve funds. If it can help settle even the unforeseen expenses, then you can hold for long.
Many reasons why some people sell short and take profit are because it gets to a point where the only means of getting money to solve their pressing needs is from Bitcoin.
I quit agree with you Ever-young. You just stated the obvious. Because someone persons might buy some coins with the intention of holding for long so it can give perfect profit. But when situation of life hits hard and there is no side pocket to foot the bill, such a person has no option than to sell and continue living. We all know that it is an established fact that 'Human wants are insatiable'. So I believe everyone going into Bitcoin investment those that with the hopes of very high returns. But we know how it is here, one must be alive before you save.
And then secondly, just as you said, a one time contract Job can pay ×5 or more of a salary earner at once. So such a person can invest more than someone who earns either daily or monthly but with little income. So for me, Bitcoin investment all depends on the available income. The better your income, the more and suitable investment you will do..